Safety limit feeler for contactless control

ABSTRACT

A control arrangement in which a pair of magnetically sensitive control elements are adapted for simultaneous actuation by a magnetic actuating member moving in proximity to but not physically engaging said elements. Actuation of either control element will cause a control function to be carried out while failure to actuate either one only of the control elements will cause an alarm circuit to be actuated.

I United States Patent [151 3,636,543 Maecker 1 1 Jan. 18, 1972 [54] SAFETY LIMIT FEELER FOR 2,793,344 5/1957 Reynolds ..340/213 UX QNT CT S CONTROL 3,017,622 1/1962 l-lorsfall ..340/282 3,339,195 8/1967 Murley, Jr. ....340/259 [72] Inventor: Kurt Maecker, Kreuzstrasse 34, 4 Dussel- 2,850,647 9/1958 Fleisher ....307/216 f, m ny 3,278,758 10/1966 Vroman ..307/216 [22] Filed: Oct 1969 Primary Examiner-John W. Caldwell [21] Appl. No.: 862,897 Assistant Examiner-Michael Slobasky Attorney-Walter Becker [30] Foreign Application Priority Data [57] ABSTRACT NOV. 15, Germany A control arrangement in a p of magnetically sensi tive control elements are adapted for simultaneous actuation ..340/259, 340/26G7683:(2)/l2/3(2) by a magnetic actuating member moving in proximity to but u o I v I a a s o o I e u u o o I q e p n [58] Flew Search g control element will cause a control function to be carried out I 7/ 6 while failure to actuate either one only of the control elements I References Cited will cause an alarm circuit to be actuated.

UNITED STATES PATENTS 7 Claims 8 Drawing Figures 1,702,997 2/1929 Ewing et al. ..340/258 t D d x 1-2 A V 2 2 X 0 L L A PATENTED JAN 1 5 I912 SHEUEUFS IN VE N TOR 70/-/ loam/re,-

PMENTEB m 1 a 522 SHEET 3 OF 5 PATENTED JAN 18 m2 SHEET 5 OF ,5

FIG. 7

FIG. 8

SAFETY LIMIT FEELER lFOR CONTACTLESS CONTROL The present invention relates to a safety limit feeler which is actuated without being contacted. Limit feelers of this type are known, and two groups of limit feelers are to be differentiated in this connection. According to the first group of such limit feelers, the devices are actuated by a permanent magnet or cam which is passed by the device. The magnetic effect may, inductively, through the intervention of a coil or by varying the resistance of a semiconductor (Hall generator, field plates); initiate a circuit or switching operation.

If desired, a Reed contact may also be affected magnetically.

This group of devices is not suitable for employment in general construction of machines, especially in the machine tool industry because the permanent magnet collects grinding dust and metal chips and holds the same whereby considerable changes in the stroke will occur which may amount from several tenths of a millimeter up to an entire millimeter.

The second group of contactless actuated devices operates with electronic oscillating circuits (initiators) while in view of the damping of the outwardly extending lines of flux, a change in the resistance is effected through some metal part whereby a circuit or a switching operation is initiated. Inasmuch as the release part such as a cam may in this instance consist of ordinary metal so that no metal dust will collect and be held, these switches are, in contrast to the first group, particularly well suitable in general machine construction and especially for machine tool controls. This is the case all the more inasmuch as they may simultaneously have very narrow tolerances as to repeat performance depending on the design and spacing up to 0.01 millimeters.

Both groups have, however, the drawback that in particular with fully electronic circuit they do not permit any outward control concerning their functions. Thus, there always exists the danger that according to both groups or embodiments unintentionally a transistor effects a control operation or brings about a switching operation which means that without outer entrance signal, an output signal is released which acts upon the device or apparatus as if it has been deliberately actuated. Above all, it should be mentioned that it may easily happen that the oscillating circuit is actuated by any foreign metal part or, on its own, also without outer influence, changes its characteristic.

It is evident that by such faulty circuit, very disadvantageous faulty controls may occur in the machine which may endanger not only the tool and the workpiece but also the health of the operator. This is particularly true when, with electronic controls, the accidental switch control of such device which is actuated without touch and contact is not noted from the outside.

It is, therefore, an object of the present invention to provide a safety limit feeler which will overcome the above mentioned drawbacks.

This object and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 diagrammatically illustrates a top view of an ordinary limit switch for a machine tool for which the arrangement according to the present invention may be used.

FIG. 2 shows a view of the head of the switch according to FIG. 1 into which head the safety device according to the invention has been built.

FIG. 3 is an electric diagram of the arrangement according to the invention.

FIG. 4 illustrates a modified circuit according to the invention.

FIG. 5 illustrates a particular design of the safety system according to the invention in the limit switch of a machine tool.

FIG. 6 illustrates another embodiment of the safety system in the limit switch of a machine tool as seen from the side.

FIG. 7 is an end view of the switch according to FIG. 6.

FIG. 8 is a top view of the switch according to FIG. 6.

The above object has been realized according to the present invention by having two control systems which, through an amplifier, for instance in the form of a transistor, thyristor-amplifier or the like, act upon a relay or a corresponding device which so controls the arrangement and are so arranged and adjusted that both have to be actuated within a predetermined set time, or if this does not occur, and alarm signal is given off through the intervention of a further amplifier.

Thus, for instance, if only one entrance control circuit is actuated or only one entrance control circuit emanates a signal in view of an inner disturbance, the entrance circuits will, to the exit transistors, convey a further input of the two control systems to the disturbance transistor through the intervention of an and and or" as well as through the reversal and through time elements.

According to a further embodiment of the invention, the entrance control circuits of the control system may be formed by oscillating circuits or magnetic field dependent semiconductors or by resistors or also magnetically influenced Reed contacts.

In conformity with a still further embodiment of the invention, it is possible for increasing the controlling safety, especially in order to avoid an unintentional or accidental switching, to give that part a particular shape which initiates the circuit, whereby it will be assured that an unintentional switching of a transistor by foreign metal parts or metallic chips will not be effected. To this end, for instance, the cam, i.e., the initiating element, will cooperate with a coulisse which is built up on the head 2 of the switch. The cam would cooperate with the coulisse in such a way and may be so designed that when being actuated the cam will move itself between the coulisse and the control surface whereby the control surface is actuated and, as the case may be, is simultaneously covered.

According to a further embodiment of the invention, the coulisse arranged at the head of the switch may be so designed that it forms a coulisse chamber in which the control surface is arranged.

The cam or the initiating part may form a U-shaped yoke one arm of which moves itself through an opening in the coulisse while actuating the control surface, whereas the other arm is connected to the movable initiating part.

According to a further embodiment of the invention, the coulisse chamber is so narrow that the chips and the dust in cooperation with the passage of the initiating part will not remain deposited in a disturbing manner.

Referring now to the drawings in detail, FIG. I shows a limit switch for a machine tool which is provided with a control head 2. The said control head has built thereinto the control systems according to the invention, in this particular instance, two oscillating circuits 3.1 and 3.2. These two oscillating circuits are, by means of the metallic part 4.1, controlled in one and/or 4.2 in the other direction. The control system is more clearly shown in FIGS. 3 and 4.

According to FIG. 3, two electronic oscillating circuits 3.1 and 3.2 are provided which act upon the transistor amplifier 6.1 which then in its turn through a relay or a corresponding element effects the control. The two oscillating circuits are furthermore provided with a trouble amplifier 13 which emanates the trouble or alarm signals.

FIG. 3 shows the condition in which the oscillating circuits are not dampened. Both oscillating circuits 3.1 and 3.2 convey their outputs A.1 and A.3 directly to the entrance of the transistor amplifier 6.1. The two other outputs A2 and A.4 are through the intervention of an or" member 5' conveyed to the second entrance E2 of the transistor or tyristor-amplifier 6.1. Thus, if one or the other of the two oscillating circuits or also both oscillating circuits operate together, if desired, they will correspondingly effect the amplifier, which amplifier 6.1 will then through a relay or a similar device effect the control.

The outputs A2 and AA are furthermore simultaneously through the reversing members 7 and 9 conveyed to the and" members 8 and 10. In the present instance, the fand members 8 and 10 at their entrance are in the position 0.l. Thus, they cannot effect a further control movement.

If, for instance, the oscillating circuit 3.1 would be dampened, in other words, if A.2 would change the value of its resistance for instance from a high value output A.2O to a low value output A.2-L, the output A.2 would shift to L. In such an instance, at 7 the reversal from L to would be effected, the and member 8 would have 0 and O at its entrance sides and would not exert a further control action. A.2 will also directly convey to the and member 10. And" member 10 would now have two inputs L and would therefore shift its output likewise to L and through the or member 11 and time member t would control the amplifier 13 which produces a trouble or alarm signal.

If now within the time period for which the time member or timer t has been set, for instance, one second, the second oscillating circuit 3.2 were likewise dampened, also the output AA would come to the position L. As a result, at the reversing member 9 there would now appear 0, and the and member 10 would have the inputs 0 and L. The and" member 10 would thus not exert a control action. Similarly, the and" member 8 will at the entrance show 0 and L. This practically means that also with the very low strokes, for instance, at 6 millimeters per minute 0.06 millimeters per second, and with possible tolerances in the spacial arrangement of the two oscillating circuits, no trouble or alarm signal would be given. The time relay has to be adjusted for this distance and the lowest answering speed.

FIG. 4 shows the same arrangement as FIG. 3 but according to FIG. 4 there is additionally checked the control of the transistor 6.]. If none of the two oscillating circuits is controlled, but nevertheless due to an interior trouble, for instance caused by the network voltage, the exit transistor 6.1 is controlled or connected through, in view of the and member 14 which at both reversing members 7 and 9 receives the entrance L, also the third entrance from exit 0.1 of the amplifier 6.1 would get an L and thus would likewise make the amplifier 13 effective. The entrance circuits of the two control systems will be bypassed.

As control circuits, also so-called slot-initiators 5.1 and 5.2 (FIG. 5) may be employed which must be actuated by a specifically shaped metallic member 6 which in the particular instance shown has the shape of a structural T-member.

In view of the special form of the metallic part, an increased safety against accidental connection by foreign metallic parts will be assured.

Referring now to FIG. 6, the limit feeler comprises a housing 1 with the conductor inlet 20. At the oppositely located side, the housing 1 has a head 2 with built-in electric oscillating circuit. The said head 2 is provided with the control surface or active surface 21 which is located in a coulisse chamber 22 formed by the coulisse 25/24. Inasmuch as the coulisse forms an almost closed chamber, it covers the control surface 21 to a considerable extent. The coulisse chamber 22 has an opening 22a through which the initiating member 25 extends into the coulisse chamber 22. The member 25 is mounted on the movable cam 26 which is clamped into a groove of the groove field 27.

FIG. 7 shows the control surface 21 as seen from the front and how it is located on the head 2.

FIG. 8 illustrates the control device of FIG. 6 as seen from the top while, for instance, the groove field moves horizontally on a milling machine table. According to FIG. 6, the groove field may also move perpendicularly with regard to the plane of the drawing.

As has been mentioned above, instead of the oscillating circuits, semiconductors or field plates (resistors) maybe employed which change their resistance when magnetically influenced. Similar remarks also apply to the application of mechanical Reed contacts which under the influence of a magnetic efi'ect close their contact or open the same, in other words, likewise indicating change in the resistance of the circuit A.1-A.2/A.3A.4.

In view of the parallel arrangement of two input circuits 3.1 and 3.2 according to the invention, a double safety of the function of the device is assured because the control of one input circuit suffices to effect an operational control through the transistor 6.1. Moreover, the safety consists in that the nonfunctioning of an input circuit, regardless for what reason, will energize a special trouble circuit which will draw the attention of the operator to the fact that somewhere some trouble occurred. The trouble circuit according to the invention may also be used directly for stopping the machine. Additionally, the checking of the operation of the amplifier 6.1 is assured.

It is, of course, to be understood that the present invention is, by no means, limited to the particular showing in the drawings but also comprises any modifications within the scope of the appended claims.

What is claimed is:

1. In a control arrangement: a relay energizable to effect a control function, a first amplifier having output terminal means connected to said relay to supply energy thereto, said first amplifier having input terminal means sensitive to a signal for causing said output tenninal means to supply energy to said relay, a pair of control elements having output terminals and sensitive to the movement of an actuating member in the region thereof for developing signals at said output terminals, an OR gate connecting said output terminals to said input terminal means of said amplifier, whereby a signal at the output terminal of either of said control elements will cause said first amplifier to supply energy to said relay, an alarm circuit including a second amplifier having input terminal means and operable to actuate said alann circuit upon the supply of a signal to said input terminal means thereof, and means connecting the output terminals of said control elements to the input terminal means of said second amplifier and operable in the absence of a signal from the output terminals of one of said control elements and the presence of a signal from the output terminal of the other of said control elements for supplying a signal to the input terminal means of said second amplifier thereby to actuate said alarm circuit, said control elements being magnetically operable and said actuating member comprising magnetic material, each control element having a further output terminal connected to the input terminal means of said first amplifier, a signal reversing component connected to each of the first mentioned output terminals of said control elements, a pair of two input AND gates each receiving a first signal from the output of the reversing component pertaining to one control element and a second signal from the said first mentioned output terminal of the other control element, an OR gate receiving the outputs of said AND" gate as inputs and having an output connected to the input terminal means of said second amplifier, a three input AND gate having an output terminal connected to the input terminal means of said second amplifier, said three input AND" gate having one input terminal connected to the output side of each said reversing component and one input terminal connected to the output terminal means of said first amplifier.

2. A control arrangement according to claim 1, which includes a time delay component interposed between the output side of said last mentioned OR gate and said input terminal means of said second amplifier.

3. A control arrangement according to claim 1, in which each control element is in the form of an oscillating circuit having a magnetic control portion, a body housing said control elements, said portions being located in side-by-side relation in an end part of said body, said actuating member comprising a magnetic member adapted for influencing both of said magnetic control portions simultaneously when brought into proximity thereto from either direction.

4. A control arrangement according to claim 3, in which said one end of said body is formed with a -shaped slot and said magnetic member is T"-shaped and is moveable in said slot.

5. A control arrangement according to claim 3, in which said one end of said body comprises an arm arranged in with a machine part.

7. A control arrangement according to claim 5, in which the slot through which said other leg moves is only slightly larger than the said other leg so the said other leg in moving through the slot will dislodge therefrom any foreign matter in the slot. 

2. A control arrangement according to claim 1, which includes a time delay component interposed between the output side of said last mentioned ''''OR'''' gate and said input terminal means of said second amplifier.
 3. A control arrangement according to claim 1, in which each control element is in the form of an oscillating circuit having a magnetic control portion, a body housing said control elements, said portions being located in side-by-side relation in an end part of said body, said actuating member comprising a magnetic member adapted for influencing both of said magnetic control portions simultaneously when brought into proximity thereto from either direction.
 4. A control arrangement according to claim 3, in which said one end of said body is formed with a ''''T'''' -shaped slot and said magnetic member is ''''T'''' -shaped and is moveable in said slot.
 5. A control arrangement according to claim 3, in which said one end of said body comprises an arm arranged in spaced relation to said magnetic control portions so as to define a slot, said magnetic member being in the form of an angle member having a portion moveable in said slot between said arm and said magnetic control portions.
 6. A control arrangement according to claim 3, in which said magnetic member is ''''U'''' -shaped and has one leg adapted to move in said slot and the other leg adapted for connection with a machine part.
 7. A control arrangement according to claim 5, in which the slot through which said other leg moves is only slightly larger than the said other leg so the said other leg in moving through the slot will dislodge therefrom any foreign matter in the slot. 